1. Field of the Invention
The present invention relates to driving assist devices, to be mounted on vehicles, capable of performing a driving assist control.
2. Description of the Related Art
There has been known a technique providing a conventional driving assist device, to be mounted on various types of vehicles, capable of performing a driving assist control. For example, such a conventional driving assist device performs a preceding-vehicle following, or preceding-vehicle following control so that an own vehicle running at a predetermined vehicle speed follows a preceding vehicle on the same lane of a roadway while keeping a predetermined vehicle distance between the own vehicle and the preceding vehicle of not less than a predetermined vehicle distance. A patent document 1, Japanese patent laid open publication No. 2005-231382 provides a conventional driving assist device capable of performing a vehicle speed control of the own vehicle so that the own vehicle is running at a predetermined vehicle speed and maintains the predetermined vehicle speed even if the driving assist device cannot recognize the preceding vehicle under the preceding-vehicle following.
By the way, the preceding-vehicle following is interrupted in various cases. For example, the preceding-vehicle following is interrupted when the driver of the own vehicle increases or decelerates the speed of the own vehicle, or an abnormality occurs in a driving assist system equipped with the driving assist device.
However, the conventional driving assist device previously described does not change the driving state of the own vehicle running at the predetermined vehicle speed when the conventional driving assist device cannot detect the preceding vehicle due to occurrence of an abnormality in the driving assist system. That is, the conventional driving assist device considers the above driving state of the own vehicle to be equal to the case in which the own vehicle is running without abnormality. It is therefore difficult for the conventional driving assist device in the driving assist system to correctly inform the occurrence of interruption of the preceding-vehicle following to the driver of the own vehicle. For this reason, when the preceding vehicle decelerates, there is a possible danger in which the own vehicle running at the predetermined speed closely approaches the preceding vehicle.